SOL currents and divertor asymmetries on COMPASS-D

On COMPASS-D, distortions in the density profile at the divertor target are observed in all discharge phases. These distortions are strongly affected by the toroidal field direction, and for B-T > 0 appear as a large asymmetr y between the inner and outer divertor regions. In this paper we investigat e the effect of both drifts and scrape-off layer (SOL) currents on divertor plasma parameters. Large currents are observed in the divertor region, whi ch change the plasma potential creating large electric fields in the divert or target. The resulting E x B drift is suggested as a possible mechanism c ausing the observed distortions. A combination of thermoelectrical and Pfir sch-Schluter terms are proposed as driving mechanisms for the SOL currents. (C) 1999 Elsevier Science B.V. All rights reserved.